Dust-free polyols

ABSTRACT

A PROCESS FOR PREPARING DUST-FREE DIPENTAERYTHRITOL, TRIPENTAERYTHRITOL AND HIGHER MOLECULAR WEIGHT POLYPENTAERYTHRITOLS, OR MIXTURES THEREOF, BY PRECIPITATING THEM IN THE PRESENCE OF METHYL CELLULOSE OR CARBOXY POLYMETHYLENE.

United States Patent Office 3,658,919 Patented Apr. 25, 1972 3,658,919DUST-FREE POLYOLS John H. Daniel, In, South Whitehall Township, Pa., as-

signor to Commercial Solvents Corporation, New York,

.Y. N Drawing. Filed Dec. 17, 1969, Ser. No. 885,953 Int. Cl. C07c 41/12U.S. Cl. 260-615 A Claims ABSTRACT OF THE DISCLOSURE A process forpreparing dust-free dipentaerythritol, tripentaerythritol and highermolecular weight polypentaerythritols, or mixtures thereof, byprecipitating them in the presence of methyl cellulose or carboxypolymethylene.

BACKGROUND OF THE INVENTION This invention relates to an improved methodfor the production of polyols. In a particular aspect, this inventionrelates to an improved process for the manufacture of dust-free di-,triand higher molecular weight polypentaerythritols.

The condensation of acetaldehyde and formaldehyde in the presence of analkaline catalyst has long been used for the manufacture ofpentaerythritol. Di-, triand higher molecular weightpolypentaerythritols, hereinafter referred to as polyols, are obtainedas by-products of this reaction. These products have importantcommercial applications, e.g. especially for resin synthesis. Whendesired they can be isolated in relatively pure form and many methodsfor so doing are known in the art. Most methods depend on the use ofrepeated precipitations-or crystallizationsfrom aqueous media. Howeverthese polyols usually precipitate in finely-divided form, usuallycrystalline, and these time crystals present problems in the separatingstep, e.g. filtering, and in drying. In subsequent manufacturing steps,the fine crystals create an objectional amount of dust when the polyolsare charged into reaction vessels for the manufacture of derivatives,e.g. resins. Accordingly a need has long existed for a method ofobtaining polyols in larger particle size than previously available.

SUMMARY OF THE INVENTION It is an object of this invention to provide animproved method for the production of polyols.

It is another object of this invention to provide a method for theproduction of dust-free di-, triand higher molecular weightpolypentaerythritols.

Other objects of this invention will be apparent to those skilled in theart from the disclosure herein.

A method has been discovered for the production of dust-free polyols,including mixtures thereof, by precipitating the polyol in the presenceof a water-soluble polymer selected from the group consisting of methylcellulose and carboxy polymethylene; when the latter is used, theprecipitation is effected at a pH below about 8.0. The precipitatedmaterial is then separated, washed and dried in accordance with knownmethods.

DETAILED DISCUSSION The process of the present invention is useful inconjunction with any of the known processes, the improvement residing ineffecting the precipitation of di-, triand higher molecular weightpentaerythritols, collectively known as polyols, in the presence ofmethyl cellulose or carboxy polymethylene in a concentration of fromabout 0.001% to about 1.0% based on the amount of the polyol.

where x is an integer of 2 or higher. The upper limit of x has not beendetermined, and it is not intended that the invention be limited to anyparticular range of x. Generally, however, x is in the range of from 2to 5 and only a small proportion of polyols is represented by theformula where x is greater than 5. The polyol must be dissolvable inwater or in mixtures of water and a water-miscible solvent, as set forthbelow, although the solutions may be relatively dilute even at elevatedtemperatures.

It will be apparent to those skilled in the art that the invention canbe beneficially applied to semi-refined or refined products simply byredissolving the polyol in a suitable solvent and re-precipitating it inthe presence of methyl cellulose or carboxy polymethylene. Generally,however, the present invention will be employed during the steps ofseparating the products of the condensation reaction.

During the condensation reaction, or upon subsequent cooling, a crudematerial consisting of tripentaerythritol and higher molecular weightpolyols precipitates from the reaction mixture. This crude material isseparated by any suitable means, e.g. by filtration, centrifugation ordecantation and is further refined as set forth below. The mother liquorcontains the monoand di-pentaerythritols which are separated bysubsequent processing steps, during which steps crude dipentaerythritolis separated by crystallization. This crude dipentaerythritol, fromwhich purer dipentaerythritol is obtained, may contain up to 50% andunder some circumstances higher amounts of monopentaerythritol.Customarily it is re-dissolved, usually in water, at an elevatedtemperature, treated with activated carbon to remove color bodies, andcooled to re-precipitate relatively pure dipentaerythritol. Theseprocessing steps are well known to those skilled in the art.

According to the present invention, the step of reprecipitatingdipentaerythritol is elfected in the presence of methyl cellulose orcarboxy polymethylene dispersed in the solution in an amount sufiicientto provide a concentration of from about 0.001% to about 1.0% based onthe amount of the polyol, preferably within about 0.0025% to 0.5%, and arange of 0.03% to 0.30% is particularly preferred. When carboxypolymethylene is used as the water-soluble polymer, the pH is adjustedto below about 8.0, if necessary. After cooling, the precipitate isseparated, preferably by filtration or centrifugation, washed and dried.

The dipentaerythritol obtained thereby is in the form of small spheres,surprisingly uniform in size, and relatively coarse compared with theproduct otherwise obtained. The improved product is more easilyseparated from the mother liquor than the product of the previousprocess and is more easily washed. When dry, it is free from problems ofdusting during handling. The bulk density is also advantageously highercompared with the product of the prior process.

The crude polypentaerythritol, mentioned above, which was separated fromthe reaction mixture after the condensation reaction was complete,contains tripentaerythritol as the major component, but tetra-, pentaandstill higher homologs are also present. The crude materials can beconveniently purified by any suitable procedure, many of which areknown. One suitable procedure is to slurry it in its own mother liquoror in fresh water, boiling to disslove solubles, filtering to remove theinsoluble portion which is rich in the higher polyols and cooling thefiltrate in the presence of the water-soluble polymer as hereinbeforeset forth to obtain a coarse, easily managed precipitate consistingprimarily of tripentaerythritol. When desired, the insoluble portion isagain slurried in water, heated to dissolve the remaining polyols andfiltered. The water-soluble polymer is added as hereinbefore set forthand the solution cooled to precipitate the polyols.

In the absence of the water-soluble polymer, the tripentaerythritoltogether with smaller amounts of higher polyols precipitate in anextremely finely-divided form which is difficult to separate from theliquid medium. The presence of the water-soluble polymer causes theformation of a coarse precipitate which presents no problems inseparation, especially filtration.

The present invention has been discussed principally as it relates tothe precipitation of polyols from aqueous solution. It is also known toprecipitate polyols from solutions obtained by dissloving the polyols inmixtures of water and water-miscible solvents. The process of thepresent invention is equally effective when used in conjunctiontherewith and it is understood that the invention is not limited to theuse of strictly aqueous systems.

In the practice of this invention, the water-soluble polymer ispreferably dispersed in water or, when preferred, in mixtures of waterand a water-miscible solvent, as is known in the art. Suitablewater-miscible solvents include the lower aliphatic alcohols that is,the lower alkanols, e.g. those having from 1-3 carbon atoms. Thedispersed polymer is added to the warm polyol solution with agitation toinsure thorough mixing. When the solution is to be filtered beforecooling, the polymer solution can be added either prior to or afterfiltration. Generally it is preferred to add it after filtration. Themixture thereby obtained is then chilled to effect precipitation of thepolyol, as is known in the art, and the precipitate is separated by anysuitable means, e.g. by decantation, centrifugation or filtration, thenwashed and dried.

'It was particularly surprising to find that effecting the precipitationin the presence of either of the two polymer types would result inincreased particle size. Watersoluble polymers often behave asprotective colloids and the usual tendency of protective colloids is tominimize crystal size. In fact numerous similar polymeric compounds havebeen tested and found to be less effective than those of the presentinvention or, more often, entirely ineffective.

Although the invention is very useful during the purification of crudedipentaerythritol or crude polypentaerythritol, its application is notrestricted to these situations. Purified dior tripentaerythritol ormixtures thereof with each other, either in the presence or absence ofmonopentaerythritol, can be crystallized according to the process ofthis invention to obtain the larger particle size and higher bulkdensity, essentially free from dusty material.

The carboxy polymethylene useful in the practice of this invention is anextremely high molecular weight crosslinked polymer of acrylic acid. 'Itis also known as a carboxy-vinyl polymer. Materials suitable for thepractice of this invention, but not necessarily limited thereto, aresold under the trademark Carbopol, by B. F. Goodrich Chemical Co.,Cleveland, Ohio. Carbopol is supplied in the free acid form under thecode numbers 934, 940 and 941, and each has an equivalent weight of 75.All of them are suitable for the practice of this invention but the 93 4resin is preferred. The performance of carboxy polymethylene isdependent upon the degree of neutralization. In general, a pH below 5.0leads to the development of a preponderance of coarsely crystallinematerial, while at a pH of 8.0 or above a finely-divided product isformed that differs little in its screen analysis from the control whereno water-soluble polymer was used.

Accordingly, when carboxy polymethylene is employed, the pH is adjusted,if necessary, to within about 3 to about 8, e.g. with an acid, asnecessary. A pH within the range of from about 3.0 to about 6.0 ispreferred and from about 3.0 to about 5.0 is particularly preferred. Anyorganic or inorganic acid capable of adjusting the pH to the desiredrange can be used for the pH adjustment. Suitable acids include, but arenot limited to, hydrochloric, sulfuric, nitric, phosphoric, formic,acetic, propionic, oxalic, etc. If the pH is below about 3, an alkalinematerial is preferably added as necessary. Suitable alkaline materialsinclude, but are not limited to, ammonia, sodium or potassium hydroxide,sodium or potassium carbonates or bicarbonates, water-soluble amines,etc. The step of adjusting pH is well known in the art and any suitablereagent can be employed in the practice of this invention.

Methyl cellulose is a well-known cellulose ether that is manufacturedcommercially in a number of degrees of substitution of the ether group.Certain of these types, particularly those having a degree ofsubstitution of 1.3 to 2.5 are soluble in cold water and to varyingdegrees also soluble in warmer water. Methyl cellulose is described in,for example, Kirk-Othmer Encyclopedia of Chemical Technology, 2nd Ed.(1964), vol. 4, pp. 648- 650. It is not intended that the invention belimited to the grades that contain only the methyl substituent. Othergrades that contain minor amounts of hydroxypropoxyl and hydroxybutoxylsubstitution in addition to the methyl groups can also be used. All ofthese substituted celluloses are effective in reducing the amount offine, dusty material in the crystal structure of the higher molecularweight polyols of pentaerythritol as herein described. A suitableproduct is sold under the trademark Methoce by The Dow Chemical Company,Midland, Mich. It is not necessary to adjust the pH when methylcellulose is employed as the polymer.

The invention will be understood more fully by reference to thefollowing specific examples. It is understood, however, that theexamples are presented for purposes of illustration only and it is notintended that the invention be limited thereby.

EXAMPLES 1 AND 2 Three samples of crude dipentaerythritol, g. each,containing 7.5% by wt. monopentaerythritol, were dissolved in boilingwater to give approximately 10% by wt. solutions. Activated carbon, 4 g.(Nuchar" manufactured by West Virginia Pulp and Paper Company), wasadded to each and the boiling was continued for 30 minutes. Each mixturewas filtered hot, then a solution of 0.03 g. of methyl cellulose(Methocel '65 Hg Standard manufactured by The Dow Chemical Co.)dissolved in 20 ml. water was added to one (Example 1) with stirring,and 0.15 g. in 20 ml. water was added to the second (Example 2); thethird received no additive and served as a control. Each mixture wasagain boiled for ten minutes, allowed to cool slowly while maintainingslow agitation until they reached room temperature, during which time aprecipitate developed in each sample.

The crystalline precipitate was separated from each sample byfiltration, washed with cold water and dried. By the use ofphotomicrographs, it was determined that the particles in the firstsample were spherical, remarkably uniform in size having diameters about0.3-0.5 mm., and the product was free from dust. The particles from thesecond example were coarse, remarkably-uniform spheres having a diameterin the range of 0.5-1.0 mm. The product was free from dust. The productfrom the third sample, the control, was not spherical but was irregularin shape and very finely divided. An appreciable amount of it was dustymaterial. The particle size distribution was determined by sieveanalysis. The screen sizes and bulk densities of the products ofExamples 1, 2 and the control are shown in the following table:

TABLE 1.EFFECT OF METHYL CELLULOSE ON PARTICLE SIZE The sphericalparticles obtained in Examplesl and 2 were found to be resistant tofracture. No appreciable change in screen analysis was noted aftershaking small amounts of the products in a 2-ounce jar for 52 hours on alaboratory shaker.

EXAMPLE 3 Crude dipentaerythritol, 100 g., having 4.96%monopentaerythritol content, was dissolved in boiling water to give a10% solution. Activated carbon (Nuchar), 4 g., was added to remove colorbodies and the mixture was boiled for 30 minutes, then filtered whilestill hot. A dilute aqueous solution of 0.01 g. (0.01% by wt. based onthe crude dipentaerythritol) of carboxy polymethylene (Carbopol-934) wasadded, followed by 1 ml. of a 0.5% solution'of NH in water. The pH ofthe resultant mixture was 4.6. The solution was cooled slowly withstirring to room temperature during which time the product precipitated.The coarse product was separated 'by filtration, then washed with coldwater and dried. The particle size distribution, determined byscreening, is given in Table 2.

The foregoing experiment was repeated in all essential details exceptthat 0.03% by Wt. Carbopol-934 was used and the was adjusted to 8.1 withammonia. Only very fine crystals were produced as shown by the followingscreen test results:

TABLE 2.EFFECT OF CARBOXY POLYMETHYLENE ON PARTICLE SIZE Carbopol-934,percent 0. 01 0. 03

Through 80 12 85 'EXAMPLE 4 The experiment of Example 1 was repeated inall essential details except that a solution of 10% by vol. of ethylalcohol in water was employed as the solvent, and the crudedipentaerythritol had a monopentaerythritol content of 13.90%. A coarse,essentially-spherical product was obtained as disclosed by examinationunder a microscope. The screen analysis is given in Table 3.

EXAMPLE 5 6 omitted. The particle size distribution determined by screenanalysis is shown in the table below:

TABLE 3 Example Percent l 4 5 i zg ig eg nosa. 0. 03 0.0 0.03

200 325 Through 325 EXAMPLE 6 Crude polypentaerythritol, consisting ofmajor proportions of tripentaerythritol and minor amounts of the higherhomologs, tetrapentaerythritol, pentapentaerythritol, etc., was obtainedby separation from a pentaerythn'tol reaction liquor prepared asfollows.

There was transferred to an open reaction vessel equipped with anagitation means and a temperature controlling means, 26,670 parts of33.6% by wt. formaldehyde solution. It was further diluted by adding36,940 parts of water. Sodium hydroxide (5,800 parts of 50% aqueoussolution) and acetaldehyde (2,9 05 parts of 99% purity) were graduallyand concurrently added to the dilute formaldehyde solution at a uniformrate such that the caustic was added over an interval of 67 minutes andthe acetaldehyde over an interval of 90 minutes. The total charge wasthen transferred to a second similar vessel where the reaction wascontinued by stirring for an additional five and one-half hours.Twenty-five hundred parts of water was used to rinse the first reactorand was added to the reaction mixture in the second vessel. Maximumtemperature during the feed cycle was 45 C., and during the reaction inthe second vessel it was 35 C.

'At the end of the reaction period, a portion, 2,550 parts, of themixture was withdrawn. It contained insoluble polypentaerythritols in afinely-divided form. The solution was allowed to stand to permit thesolids to settle and the clear liquor was removed by decantation,leaving a residue of 650 parts of the slurry. The residue was heated toboiling to dissolve most of the precipitate and filtered while still hotwith the assistance of a filter aid. The filtrate was cooled to C. and0.009 parts by weight of methyl cellulose (Methocel) was added, followedby gradual cooling to 35 C. The polypentaerythritols separated as coarseagglomerated particles that filtered readily.

The foregoing experiment was repeated in all essential details exceptthat the methyl cellulose was omitted. Only a very fine productseparated from the cooled solution; this was difficult to filter andupon drying yielded a dusty product.

EXAMPLE 7 The experiment of Example 1 is repeated except thatapproximately 1.0% of methyl cellulose is substituted for 0.03% of same.A coarse precipitate, readily filterable and dust-free when dried, isobtained.

I claim:

1. In a process for the production of a substantially dust-free polyolrepresented by the formula:

(3112011 HO- -CH2C-CH20]H CHzOH where x is an integer of 2 or higher, byprecipitation from about a 10% by weight solution in water, or in anaqueous lower alkanol solvent containing it, by cooling said solutionthereby precipitating said polyol, the im- 7 provement comprisingeffecting said precipitation in the presence of methyl cellulose, in anamount of from about 0.001% to about 1.0% based on the weight of saidpolyol thereby producing said substantially dust-free polyol havingenlarged particle size.

2. The process of claim 1 wherein said methyl cellulose is employed inan amount of from about 0.0025% to about 0.5% based on the weight ofsaid polyol.

3:. The process of claim 2 wherein said methyl cellulose is present inan amount of about 0.15% based on the weight of the polyol.

4. The process of claim 1 wherein said polyol is tripentaerythritol.

5. The process of claim 1 wherein said polyol is dipentaerythritol andsaid polymer is methyl cellulose in an amount of about 0.03% to about0.30% based on the weight of said polyol.

References Cited UNITED STATES PATENTS 6/1956 Brendlein et al. 260-615 RFOREIGN PATENTS 10/1963 Japan 260-615 R 11/1969 Japan 260-615 R HOWARDT. MARS, Primary Examiner us. 01. MR.

mg UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No.3,658,919 Dated A pril 2 5, 1972 Inventor(s)v Jnhn H Dan-IP1 .TY'

It is certified that error appears in the above-identified patent andthat said Letters Patent are hereby corrected as shown below:

Column 2, line 69 "rials" should be rial.

Column 3, line 20 "dissloving should be dissolving-.

Column 4, line 34 Methocel" should-be --"Methocel"--.

Column 5, line 11, Table 1, under the heading Example 2,

"29.2" should be --29.0

Column 5, line 12, Table 1, under the heading Example 2,

"68.1" should be ---;Qa.7--.

Column 5, line 13, Table 1, under the heading Example 2,

1 "1.0" should be l.2--.

Column 5, line 14, Table 1, under the heading Example 2 "1.7" should bel.l-.

Signed and sealed this 27th day of February 1973.

(SEAL) \ttest:

EDWARD M. FLETCHER,JR. ROBERT GOTTSCHALK \ttesting Officer Commissionerof Patents

